单项选择题
A.大于B.小于C.等于D.随意整平
A.20m ×20mB.30m ×30mC.40m ×40mD.50m ×50m
A.0.1%~0.2%B.0.2%~0.3%C.0.3%~0.4%D.0.4%~0.5%
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